Process for producing water absorbent resin

Abstract

The present invention relates to a process for producing water absorbent resin comprising a step of adding a high-molecular crosslinking agent which has at least 2 azetidinium salt groups in the molecule and has at least 1000 weight-average molecular weight to the water absorbent resin paticles having carboxylic groups and carboxylic acid salt groups and a step of efficiently crosslinking the vicinity of the surface of the water absorbent resin particles. In the process for producing water absorbent resin according to the present invention, the use of high-molecular crosslinking agent achieves less permeation of the crosslinking agent into the water absorbent resin particles and enables efficient crosslinking of the vicinity of the surface of the water absorbent resin particles. Consequently, the water absorbent resin having high water absorbency both under pressure-free state and under loading can be manufactured. Because the crosslinking agent contains a large amount of azetidinium salt groups highly reactive to carboxylic acid groups or carboxylic acid salt groups in the molecule, the water absorbent resin having high crosslinking efficiency, good safety, and good flowability can be manufactured.

What is claimed is: 
     
       1. A process for producing water absorbent resin comprising a step of adding 0.01-10 parts by weight of a high-molecular crosslinking agent (B) which has at least 2 azetidinium salt groups in the molecule and has a weight-average molecular weight of at least 1000 to 100 parts by weight of water absorbent resin particles (A) which have a carboxylic acid group and/or carboxylic acid salt group and a step of heat-crosslinking the vicinity of the surface of the water absorbent resin particles (A). 
     
     
       2. A process for producing water absorbent resin according to claim 1 comprising a step of adding 0.01-10 parts by weight of the high-molecular crosslinking agent (B) and 0.1-10 parts by weight of the 2-70 wt % aqueous solution of a water soluble compound (C) to 100 parts by weight of the water absorbent resin particles (A) and heat-crosslinking the vicinity of the surface of the water absorbent resin particles (A); wherein the water soluble compound (C) is at least one compound selected from the group consisting of alkylene-oxide adducts of monofunctional alcohols and lactams, and is inert to the water absorbent resin particles (A) and high-molecular crosslinking agent (B).   
     
     
       3. A process for producing water absorbent resin according to claim 1, wherein the weight-average molecular weight of the high-molecular crosslinking agent (B) is 5,000-100,000. 
     
     
       4. A process for producing water absorbent resin according to claim 1, wherein the high-molecular crosslinking agent (B) possesses at least 4 azetidinium salt goups in a molecule. 
     
     
       5. A process for producing water absorbent resin according to claim 1, wherein the high-molecular crosslinking agent (B) does not contain any amide group in a molecule and is a condensation product of high-molecular polyamine having at least 4 secondary amino groups with epihalohydrin. 
     
     
       6. A process for producing water absorbent resin according to claim 1, wherein the ratio of the high molecular crosslinking agent (B) to the water absorbent resin particles (A) is 0.05-5 wt %. 
     
     
       7. A process for producing water absorbent resin according to claim 1, wherein the temperature of heating for crosslinking is 80°-180° C. 
     
     
       8. A process for producing water absorbent resin according to claim 1, wherein the water absorbency under a pressure-free state of the obtained water absorbent resin is 55 g/g to 100 g/g and the water absorbency under loading is 35 g/g to 60 g/g. 
     
     
       9. A process for producing water absorbent resin according to claim 1, wherein the water absorbent resin obtained by the process is useful as a water absorbing agent for hygienic materials.